NSWCCR/RDTR-08/22 Report date: 16 April 2008

“A New Coating Process for Production of Coated Magnesium Powders” Scientific and Technical Report

Contract #: N00164-07-R-6068

Applied Thin Films, Inc. 1801 Maple Ave Suite 5316 Evanston, IL 60201-3135

NSWC Crane Technical POC: Caroline K. Wilharm Code WXRL, Bldg. 121 Crane Division, Naval Surface Warfare Center 300 Hwy 361 Crane, IN 47522-5001

Applied Thin Films, Inc.

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16 APR 2008

00-00-2008 to 00-00-2008

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5a. CONTRACT NUMBER

A New Coating Process for Production of Coated Magnesium Powders

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Applied Thin Films, Inc.,1801 Maple Ave,Suite 5316,Evanston,IL,60201-3135 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES)

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Executive Summary This phase III project focused on the development of a pre-production scale process for the deposition of aluminophosphate coatings on 1-lb batches of magnesium powder to passivate the magnesium against moisture-induced degradation. Work conducted in the prior Phase II effort was successful in the development of a laboratory-scale coating process for 30g batches of atomized magnesium powder. This work focused on two primary tasks: 1) development of the coating process to provide protection for ground magnesium powder similar to that achieved for atomized material in Phase II, and 2) increase the batch size to demonstrate feasibility of production and to provide larger quantities of material for validation and testing. Four primary areas of focus in the project were: 1) Installation and set-up of coating equipment and supporting infrastructure 2) Coating process development for the deposition of high-quality coatings on ground and atomized magnesium powder in 1-lb batches 3) Characterization and evaluation of performance for 1-lb batches of coated magnesium 4) Production and delivery of 55 pounds of coated magnesium powder of three atomized and one ground powder types During this project, a coating system suitable for the deposition of the Cerablak®-based coating on 1-lb batches of powder was installed, and the supporting infrastructure was designed and constructed. Process parameters for the coating deposition were developed in order to achieve high-quality coatings on both atomized and ground magnesium powder. A strong effort was oriented toward the adaptation of the coating process for the ground magnesium powder, and a major improvement in the performance of coated ground magnesium powder against moistureinduced degradation was achieved. Powder produced as deliverable for this project was characterized for metallic magnesium content, magnesium hydroxide content, and performance against humidity-based aging. Coated atomized powders showed little or no reduction in metallic magnesium content during coating and decreased magnesium hydroxide content compared to the uncoated powder of the same type. Performance of atomized powder in humidity-based aging showed reduced hydroxide formation compared to uncoated powder for a given exposure, and fine-mesh powders showed the greatest improvement in performance with a rate of degradation less than one half that of the uncoated material. The performance of coated ground magnesium powder, RMC-200BS, was dramatically improved during this project. Performance against humidity-based aging shows a highly stable initial period that is not present with uncoated ground magnesium. Although analysis of the ascoated ground powder shows a small residual content of magnesium hydroxide, on the order of 3 wt%, there appears to be little other loss of metallic magnesium due to the coating process. Under the accelerated aging conditions used in this work, uncoated ground magnesium rapidly degraded to a hydroxide content exceeding that of the coated material, and the coated material maintained a highly stable hydroxide level for over twice that period of time. This should provide increased shelf-life and minimize losses in combustion reliability. The final deliverable containing 10 lb of coated -325 mesh atomized powder, 5 lb of coated 200/325 mesh atomized powder, 15 lb of coated Gran 16 atomized powder, and 25 lb of coated RMC-200BS ground magnesium powder was produced and delivered at the conclusion of this work. Applied Thin Films, Inc.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Overview Issues related to the interaction of moisture with magnesium-based pyrotechnic compositions have historically been a problem. The interaction results in the loss of metallic magnesium available for combustion and the production of hydrogen gas as a by-product that presents a potential hazard for inadvertent ignition. ATFI developed a laboratory-scale phosphate-based inorganic coating for the protection of magnesium from moisture during a previous Phase II project which showed promise for atomized magnesium powder. This Phase III project sought to increase the batch size from the previous lab-scale 30g batch to a pre-production 1-lb batch size and to extend the protection to ground magnesium powder as well as atomized. This scientific and technical report covers the work carried out during the originally specified 6 month period of performance from July 6, 2007 through January 6, 2008 and during the no-cost extension from January 6, 2008 through April 6, 2008. The work performed under this project is documented according to the project tasks as outlined in the contract and outlined in the task plan below (see Table 1). In brief, Task 1 involved the construction and assembly of the coating system and supporting infrastructure, which was used for the scale-up and production of 1-lb batches of coated magnesium powder. Task 2 focused on the process development required to scale batch sizes from the Phase II batch size of 30g to the desired pre-production batch size of 1-lb. The powder produced in task 2 was analyzed in task 3 to determine the characteristics of the as-coated material and the moisture-induced aging behavior. Finally, task 4 focused on the delivery of the 1-lb batches of coated magnesium, which constituted the final deliverable of the Phase III project. During the course of the original period of performance, initial 1-lb batches of each powder type were prepared at the end of the scale-up process, Task 2. A 3-month no-cost extension was requested in order to characterize the aging behavior of those powders over a time sufficient to benchmark their performance and provide a baseline for the production batches. During this time a strong effort was also placed on improvement of the performance of coated ground magnesium, and a major improvement of performance was achieved. The final deliverable, 55lbs of coated magnesium powder, was shipped to NSWC Crane on March 31, 2008.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Table 1: Project task plan and schedule

Task

JulAug

SepOct

NovDec

1.0 Identify, Operate, and Optimize Equipment for Increased Batch Size 2.0 Scale-up of Batch Size for New Coating Process up to 1 lb 3.0 Coating Performance Evaluation and Materials Characterization 4.0 Delivery of 1-lb Batches of Coated Magnesium

Task 1: Identify, Operate, and Optimize Equipment for Increased Batch Size Task 1 encompassed the construction and testing of a scalable coating system capable of producing 1-lb batches of coated powder. This work was completed during the initial phase of this work and served as the basis for the scale-up work in the subsequent tasks.

Task 2: Scale-up of Batch Size to 1 lb for New Coating Process Following the successful testing of the coating system with pure solvent and pure coating solution, the scale-up process was begun for coating atomized magnesium powder. Initial 100g batches of powder (-325 mesh atomized) were coated using coating parameters transferred from the smaller coating system used previously for laboratory coating in the previous phase II work. The coated powder was analyzed primarily by SEM in order to estimate coating quality and coverage as well as uniformity throughout the batch. Although only small amounts of powder can be sampled in the SEM, effort was taken to obtain representative material for analysis. As seen below in Figure 1, initial batches of Mg powder that were coated did not exhibit the desired uniform coverage observed in previous lab-scale batches under similar parameters.

Process changes were incorporated into subsequent

batches to address these differences, and coating quality and uniformity were systematically improved.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008

Figure 1: SEM images of magnesium powder coated in 100g batches with new coating procedure. The left image is representative of early coating runs typified by poor coverage of Mg powder. The image above right is typical of later runs with much better coverage of the Cerablak™ coating. Following the initial assessment of the coating quality by SEM and EDS, coated powder batches were analyzed by nitrometer and TG/DTA to assess magnesium content of the coated powder, magnesium hydroxide content, and apparent barrier properties toward nitride formation at elevated temperature. As anticipated, the processing parameters for the coating of powder in the larger coating system required adjustment as the batch size increased in order to compensate for the coating vessel surface area and increasing demand on the heating and cooling systems. This process was repeated for each magnesium powder type to obtain proper process parameters necessary to achieve high coating quality.

Task 3: Coating Performance Evaluation and Materials Characterization Characterization of initial 1-lb batches of as-coated powder Particle Size Due to the thin and highly conformal nature of the coating, the particle size distribution of the asreceived powders is substantially retained in the coated powder. Powder specifications in terms of particle size are established through pass/retention statistics on sieves with particular mesh sizes. Although the precise distribution of the powder particle sizes was not compared, all coated powders in this work still passed through the sieve corresponding to the largest particle size in the as-received magnesium powder. This result confirms that there is no significant agglomeration in the powder, at least for the larger particles. Applied Thin Films, Inc.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008

ATFI Proprietary and Confidential

Figure 2: Coated -325 Mesh atomized powder produced during phase II (left) and phase III (right). Under equivalent post-processing, the current powder shows much less agglomeration and a finer texture.

Coating Quality Criteria used to establish the coating quality for all powder grades was the visual indication of a coating in the SEM images and the identification of the Cerablak® elemental signature in EDS spectra obtained from various areas of the sample. Good coating coverage was identified for all four magnesium powder grades, as exemplified in Figure 3 for the -325 mesh atomized powder.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Uncoated -325 Mesh Atomized Magnesium Powder

Coated -325 Mesh Atomized Magnesium Powder

Cerablak® signature in the EDS data

Figure 3: SEM and EDS results for coated versus uncoated -325 mesh atomized magnesium powder. Little change in the particle morphology is noted due to the conformal nature of the coating and uniform coverage; however, the characteristic signature of the Cerablak® coating is observed in the EDS spectrum indicating the presence of the coating. Available Metallic Magnesium Following confirmation of good coating coverage of the powder, additional testing was carried out in order to ensure that no significant reduction of metallic magnesium content occurred during the coating process. This analysis was carried out using a nitrometer; and although the accuracy of the nitrometer is only approximately ±5% in our laboratory configuration, comparison of as-received powder to as-coated powder could detect any substantial changes that occurred during the coating process. For the atomized magnesium powder grades, no statistically relevant degradation was observed. As discussed below, the analysis of the coated Applied Thin Films, Inc.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 ground powder showed a small decrease in available metallic magnesium which results from the different process used for coating of the ground powder. Moisture-Induced Degradation Overview The performance of the Cerablak® coating as a barrier toward atmospheric moisture induced aging was tested for the initial 1-lb batches of coated powder. Samples were introduced into a controlled-humidity chamber which maintained conditions of 50°C/55%RH, and the powder was periodically tested by TGA in order to assess the magnesium hydroxide content of the aged powders. While this technique does not directly measure the metallic magnesium content of the powder, it is sensitive toward magnesium hydroxide formed during reaction between metallic magnesium and water vapor during aging. This technique was favored over nitrometer testing, which was used in the earlier Phase I and II work, due to the greater sensitivity. Atomized Powder Due to the relatively slow aging characteristics of some of these atomized powders under the aging conditions of 50°C/55%RH, aging of the initial 1-lb batches of coated powder was followed for two months. This period of time was considered sufficient to determine whether any negative influence of the coating on the aging process was observable before production of the required deliverable was initiated. For all powders tested, the measured degradation was the same as, or lower than, the uncoated powder of the same type. Due to the time required to complete this aging analysis, it was necessary to pursue a 3-month no-cost extension which was processed in December of 2007 and which moved the project completion date to April 6, 2008. Based on the positive aging results for the initial 1-lb batches of each atomized powder type, production of the deliverable quantity of each powder was started. Ground Mg Powder Initial testing of the coated ground powder, RMC200BS, indicated poor performance during aging under accelerated conditions, which was consistent with the results obtained in the Phase II effort. Despite the reduced agglomeration of the powder produced using the new coating procedure, the aging performance showed an increased rate of moisture-induced degradation compared to the uncoated material.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Following these initial results, a significant research effort was focused on improving the performance of the 1-lb batches of ground Mg powder. As shown in Figure 4, the performance of coated ground Mg powder under accelerated aging conditions of 50°C/55%RH was improved dramatically compared to the performance of the powder from the previous Phase II project (Phase II powder is shown as coating variant 1). Because the degradation of uncoated ground Mg powder is rapid under our exposure conditions, 5 days of exposure was sufficient to gauge the performance of new coating variants. The variant that was adopted for the production of the deliverable coated ground powder is shown as “Variant 5” in Figure 4. This variant allows for a small percentage of Mg(OH)2 in the as-coated material; however, it advantageously results in an extended period of stable performance as shown in Figure 5. Following longer exposure times at 50°C/55%RH, the period of stable performance eventually gives way to hydroxide formation, but the net result is performance that is much more stable initially and a resulting degradation that is significantly lower than that of the uncoated powder after about 7 days of aging. The approaches taken were successful in reducing the initial period of accelerated aging that was present in the Phase II powder. Although further performance improvement could be expected by continuing the approaches we took as well as optimization of coating quality, the impact of the coating on other relevant properties such as burn-rate, sensitivity to ESD and the like also should be considered when optimizing the coating. These properties will not be determined until after delivery of the first batches of powder to NSWC Crane at the conclusion of this project.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Progress in RMC200BS Coating Performance 30% Variant 1 Variant 2

25%

Variant 3 Variant 4 Variant 5

Wt. % Mg(OH)_2

20%

15%

10%

5%

0%

0

1

2

3

4

5

6

Days of Exposure at 50C/55%RH

Figure 4: Magnesium hydroxide formation, as determined by TGA, for 5 coating variants on RMC200BS ground Mg powder before and after exposure to accelerated aging conditions of 50°C/55%RH. Coating variant 1 represents the performance of material produced during the Phase II project, and variant 5 represents the material produced under this Phase III project.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 Humidity Aging of RMC200BS Mg Powder Variant 5 25.00%

Uncocated Variant 5 Batch 1

Wt. % Mg(OH)2

20.00%

Variant 5 Batch 2

15.00%

10.00%

5.00%

0.00%

0

5

10

15

20

25

Days of Exposure at 50C/55%RH

Figure 5: Magnesium hydroxide formation during exposure to accelerated aging conditions of 50°C/55%RH, as determined by TGA, for RMC200BS ground Mg powder coated using variant 5 as compared to uncoated powder of the same grade. Characterization of Production 1-lb Batches Characterization of the initial 1-lb batches of coated powder was used to establish baseline data for the specification and performance of the production batches of each powder type. Based on the baseline data and the coating parameters established in Task 2, the deliverable quantity of each type of magnesium powder was produced in 1-lb batches. The powder types were produced sequentially beginning with the atomized powders and ending with the ground powder. Process parameters were carefully recorded during the coating process for each batch, and all anomalies were flagged for review. This provided for a high degree of reproducibility for the coating process itself. As-coated powders were tested via nitrometer for metallic magnesium content and by TG/DTA for magnesium hydroxide content. Significant deviation of those characteristics from those of the initial 1-lb batches indicated a problem with that production batch, and those batches were discarded from the final deliverable. This procedure resulted in a high degree of confidence in the reproducibility of the individual powder batches, and this reproducibility was reflected in the subsequent aging performance. Applied Thin Films, Inc.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 The final test criteria for the coated powder was the rate of degradation upon exposure to accelerated aging conditions of 50°C and 55%RH. As described previously, samples were introduced into the aging chamber and tested periodically for magnesium hydroxide content. The quantity of magnesium hydroxide after a given exposure time was compared to that of uncoated powder and the initial 1-lb batches of the same type. This process was carried out on every 3rd batch of powder produced, which provided a statistical measure of the performance of the entire deliverable. As seen from the data for the various powder types (see below), the aging performance of the batches was highly reproducible, and the statistical sampling of every 3rd batch provided reliable data for each powder type. The above data was collected for each powder type and are included in Figure 8 to Figure 10 below. This data can be referenced to the deliverable powder batches through the powder type and batch numbers included for each 1-lb batch of powder delivered under this contract. As-coated Characterization Data for Atomized Powders As reported above, 1-lb batches of coated powder were analyzed by nitrometer for metallic magnesium content and by TGA for magnesium hydroxide content. Nitrometer analysis allows for the determination of metallic magnesium in a given sample through the production of hydrogen gas upon reaction with acid. Due to errors involved in the measurement that are dependent on the apparatus and the particular powder type, the accuracy of the data can vary significantly. The accuracy of the measurement for the fine-particle size powder was inherently better than that for the larger particle size powders as can be seen in Figure 6 below. For the -325 mesh and 200/325 mesh powders, it is estimated from this data that there is less than 5 wt% difference in the amount of metallic magnesium in the coated powder versus the uncoated powder, and approximately 3% of this weight difference can be accounted for by the Cerablak®-based coating. For the Gran 16 powder, the scatter in the data is quite large, and an accurate determination of metallic magnesium content is difficult due to the large scatter in the data; and it is useful to instead look at the TGA data for magnesium hydroxide content. TGA analysis of the as-coated powders is a reproducible and accurate method for the determination of magnesium hydroxide content. This data for each of the deliverable 1-lb batches of atomized powder is shown below in Figure 7. The error inherent in the analysis when small quantities of magnesium hydroxide are present in a magnesium sample makes accurate determination below 1 wt% difficult; however, it can be seen from this data that the magnesium hydroxide content of the as-coated atomized powder batches lies below 1% [a Applied Thin Films, Inc.

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NSWCCR/RDTR-08/22 Report date: 16 April 2008 baseline error in the measurement of batch #5 of -325 mesh atomized powder is responsible for the high value seen in the figure, and subsequent analysis suggested a more reasonable value